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Abstract

Objectives: To investigate the influence of motor control training of deep external rotators of hip joint on pain and function followed by Total Hip Replacement (THR). Methods: Subjects (n=10) who had posted for unilateral Total Hip Replacements were enrolled. Pre and post intervention data collected from 10 patients, who were posted for total hip replacement. Patient’s received motor control training for deep external rotators of hip joint, twice a day for 8 weeks along with standard THR rehabilitation exercises. Thirty second chair stand test is used as primary outcome measure and NPRS, HOOS and Timed Up and Go test are used as secondary outcome measures. All the outcome measures have taken pre and post 8 weeks of intervention. Paired t-test used for statistical analysis to find out the changes within the group. Results: Overall significant differences were observed before and after the training in all outcomes. 30 sec chair stand test improved by mean of 2.60 ± 1.35 times (p=0.001). NPRS demonstrated a reduction in pain score from 8.90 (0.99) to 2.30 (0.82) with a mean of 5.60 ± 0.96. Timed Up and Go test showed an improvement of 8.10 sec over an 8 weeks from 29.60 sec to 21.50 sec (p=0.003). HOOS total score showed a better shift from 98.89 ± 16.59 to 52 ± 8.92 in 8 weeks. Conclusion: The implementation of motor control training of deep external rotators of hip joint along with standard THR protocol following unilateral Total Hip Replacement improves pain scores and physical function post 8 weeks of surgery.

Keywords

Introduction

Total Hip Replacement (THR) is a surgical procedure performed
for osteoarthritis, avascular necrosis and any infectious
conditions affecting hip joint. [1,2] It involves surgical excision
of neck of femur and acetabular cartilage which is replaced
with prosthetic components. [3] Pain, decreased range of motion,
impaired postural stability and mobility are followed with the
surgery. [4,5] A systematic review on post THR rehabilitation
describes the post THR rehabilitation exercises consisting of
ankle toe movements, quadriceps and gluteal sets, hip range
of motion exercises, early mobilization and after 8 weeks,
the rehabilitation includes weight bearing exercises and hip
abductor muscle resistance training. [1]

An interview based study conducted on postoperative THR
standard rehabilitation found that exercises prescribed
by physiotherapists include quadriceps and hip abductor
strengthening, bridging, range of motion exercises and weight
bearing exercises. [6] A randomized controlled trial by Jan et al.
[7] on home exercise post THR describes the exercise which
consists of isotonic strengthening exercises for hip flexors,
abductors and extensors with low resistance and 30 minutes
walking every day. [7] However analysis of gait, squat manuever
and limb loading of post THR patients suggest that dynamic
instability persists in this group of individuals even after
standard rehabilitation. [8]

For a functionally pain free stable joint, active control of hip muscles are essential. The hip joint stability is contributed by
active, passive and neural subsystem. The deep muscles of hip
joint contribute to it majorly by closely acting to its axis and
gives compression force. The main deep muscles of hip joint
includes gamelli superior and inferior, obturators internus and
externus, and quadratus femoris, which also functions as the
hip external rotators. [9] Studies on cadaveric specimen found
that posterior capsule of hip joint is reinforced with obturator
externus contributing to hip joint stability. [10] Dysfunction
associated with these muscles makes the joint less stable and
painful and rehabilitation specifically targeting these muscles
improve function and alleviate pain. [9]

Contraction of the local musculature is considered a feed
forward strategy of the nervous system. It prepares the joint for
pertubations caused by the limb movement. [9] Research shows
that pain alters this feed forward strategy and causes rapid
atrophy of local muscles. [11] Deep location and proximity of
these muscles to sciatic nerves makes difficult to get an accurate
electromyogrphic data of their dysfunction.9 Evidence of hyperactivation
of global muscles after THR suggests a compensatory
mechanism for the local muscle dysfunction. [12]

Motor control is defined as the ability to regulate or direct
the mechanisms essential for the movement. [13] Motor control
training involves 3 stages: stage of conscious/cognitive, stage
of associative/repetition and stage of automatic. The cognitive
stage required high levels of awareness from the subjects. It
is augmented with visual, verbal and tactile cuing from the
therapist, normal breathing pattern and a good understanding
about the movements by the subject. This stage retains the
activation of local muscle system during the movement. The
stage of association primarily involves identification and
correction of faulty movements. This stage helps therapist to
identify the movement faults and break them into small parts.
This followed by repetition of movements in the corrected
manner. The final step is incorporating the corrected movements
into the functional tasks of daily living. [14]

Sims et al. [15] reported higher gluteus medius EMG firing in
subjects with unilateral hip osteoarthritis. A study by Agostini
et al. [12] observed altered muscle activation and timing patterns
in gluteus medius even after THR. Retcheford et al. [9] proposed
that local muscle dysfunction is present in the joint associated
with pain and pathology. A specific muscle retraining can
restore the muscle function in those joints. The hip joint stability
can be enhanced by retraining the deep external rotators of hip.
The local muscle activation facilitates the effectivness of the
other standard rehabilitation exercises. Thus evidence supports
activation of these muscles before global muscle training. [9]

Standard THR protocols are having no components to
rehabilitate motor control dysfunction of deep external rotators
of hip. There is a paucity of literature for motor control exercise
of deep external rotators of hip. Hence this study aimed to
investigate the influence of motor control training of deep
external rotators on pain and functional performance in subjects
who have undergone unilateral THR.

Materials and Methods

A total of 13 subjects who were referred for THR were screened
for inclusion and 10 subjects were recruited for the study. The
inclusion criteria was unilateral THR and age between 40
to 85 years. [3] subjects were excluded from the study due to
bilateral and revision THR, hemiarthroplasty, THR following
hip fractures and neurological conditions which affects patients
ability to understand and follow commands such as stroke,
parkinsons disease. Sample size calculated as 10, based on 30
sec chair stand test with power of study as 80% anticipating
MCID of 3 stands with standard deviation of 2.6. The primary
outcome measure used was 30 sec chair stand test (30 sec
CST). The secondary outcome measures includes Numerical
Pain Rating Scale (NPRS), Hip disability and Osteoarthritis
Outcome Score (HOOS) and Timed Up and Go test (TUG). The
study was approved by the Institutional Research Committee
of School of Allied Health Sciences, Manipal Univeristy, India
and conducted at Manipal Hospital, Bangalore. The subjects
were screened and those who met the inclusion criteria were
recruited. The purpose of the study was explained and informed
consent was obtained. The recruited subjects were assessed
at baseline pre-operatively with both primary and secondary outcome measures. Posterolateral approach is the common
approach used, which preserves the abductor mechanism of hip.
To access the hip joint the gluteus maximus is split in line with
the muscle fibers and the deep external rotators are transected
near its insertion. It preserves the integrity of the gluteus medius
and vastus lateralis. In order to dislocate the hip joint the
posterior capsule is incised thus leading to a higher incidence
rate of joint instability and dislocation of hip postoperatively. [16]

Postoperatively subjects received an intervention which
involved standard THR protocol along with motor control
training for deep external rotators of hip joint. Intervention took
place daily till the subject got discharged and after that twice a
week for 8 weeks, with each session lasting for 20-30 minutes.
The therapist supervised the subjects through telephone once
a week for 8 weeks to maintain the continuity of intervention.
The subjects underwent another set of assessment of the same
outcomes after 8 weeks.

The intervention began within 24 hours after surgery and took
place twice a day till discharge. Most of the patient received
pain medication and cryotherapy for pain management postsurgery.
On an average most of the patients got discharged
from hospital after 8 days. Subjects were asked to perform
two sets of 10 repetition lasting 10 sec. There was a 30 sec
break between sets. To target the posterior fascicles of psoas
major, obturator internus and externus, gemelli superior and
inferior muscles, the subject was asked to lie in supine and to
mentally visualize and approximate the head of femur into the
acetabulum without tilting the pelvis. For a better understanding
of the exercise, patients were practiced it first in normal leg and
after familiarisation they were performed it on the operated leg.
[17] [Figure 1]. For the quadratus femoris muscle subject was in
supine lying and asked to mentally visualize two points on either
side of hip (lateral to the hip joint) at the level of the greater
trochanter and approximate them with minimum contraction of
the buttocks (gluteus maximus). [17] [Figure 2].

The statistical analysis was done using SPSS software (version
16.0; SPSS. Chicago, IL, USA). Paired ‘t’ test was used to
assess the difference within the group with confidence interval
set as 95% and p value of <0.005

Results and Discussion

A total of 10 subjects (7 males and 3 females) who had undergone
unilateral THR with mean age 60.60 ± 14.93 years were
included in our study. Seven subjects underwent THR as a result
of OA and the remaining was having AVN of head of femur. The
demographic and baseline data of the subjects is given in Table
1. 30 s chair stand test in the present study changed from 6.80 to
9.30 with a mean of 2.60 ± 1.35 times, which was statistically
significant (p< 0.001). NPRS demonstrated a reduction in pain
score from 8.90 (0.99) to 2.30 (0.82) by a mean of 5.60 ± 0.96
points.

Table 2: Within group analysis of all outcome measure after 8 weeks of intervention.

Discussion

The present study aims to find the influence of hip muscle motor control training on pain and function following unilateral total
hip replacement. 8 weeks motor control training improved the
outcome measures in our study.

The primary outcome measure 30 sec chair stand test changed
from a baseline measure of 8 to 9 stands with a mean difference
of 2 stands. The observed change was clinically significant
since the MCID of 30 s CST is 2-3 stands.[18] A study done by
Mikkelsen et al. [19] to evaluate the effect of early progressive
resistance training in subjects who had undergone unilateral
THR found a mean change of 2 stands in 30 s CST in the
intervention group. The progressive resistance training group
had received 2 days of supervised resistance training and 5 days
of unsupervised home exercises from the first week of surgery
for 10 weeks. The observed improvements in Mikkelsen et al.
[19] study may be due to increased hip muscle strength whereas,
in our study motor control training of hip muscles demonstrated
the same result in a comparatively shorter duration. This may
indicate higher muscle recruitment of hip stabilizers and thus
shortened the duration for recovery [20]

The NPRS score for pain intensity in the present study reduced
post 8 weeks of intervention by a mean difference of 6 point
from the baseline score of 8.90. The MCID for NPRS was
reported as 3 points; and current study demonstrated a change
of 6 points which was a clinically significant.[20] A multicenter
randomized controlled trial by French et al. [21] to test the effect
of manual therapy with exercises on hip OA observed a mean
change of 1.82 points after 9 weeks of intervention. These 5
days sessions in each week consists of 30 min of stretching,
strengthening, generalized body exercises and 15 min of manual
therapy sessions. It shifted the NPRS score from 6.02 to 4.20 after
9 weeks of intervention. The manual therapy interventions (low
grade hip joint mobilization) may have caused micro-trauma of
soft tissues and prevented the pain score to change significantly.
The comparatively major improvement in pain score in the present
study may be due to motor control training of hip muscles. It may
have prevented the uncontrolled movement between the articular
surfaces of the hip joints during daily activities. In addition to that
the muscular dysfunction present between local and global muscle
systems of hip after THR may be reduced by the motor control
training. Collectively it helps to prevent micro-trauma; thus leading
to a major shift in pain score.

Timed up and go test of the present study improved from 29.60
sec to 21.50 sec with a mean difference of 8.10 sec. A randomized
controlled trial on a center based postoperative rehabilitation in
subjects who had undergone unilateral THR demonstrated an
improvement in TUG after 8weeks of intervention. The time
duration reduced from a baseline measure of 13.5 sec to 11.1 sec
with a mean difference of 2.4 sec. [22] The center based group had
received exercise focused on functional tasks, daily living tasks,
balance, strength and endurance which was delivered 5 sessions
in a week. The variety of exercises to the center based group may
have resulted in better strength and balance. At the same time
comparatively larger difference in TUG in the present study may
be due to the higher baseline of 29.60 sec compared to 13.5 sec
of the center based group. This change may indicate increased
muscle size and higher muscle activation of hip external rotators
during TUG. A study by Mendis et al. [23] to test the effect of
motor control in subjects with and without low back pain found
that 8 weeks of motor control training increased the hip muscle
size and prevented hip muscle atrophy.

The HOOS pain sub-scale had improved from a baseline
of 34.25% to 68.25% with a mean difference of 33%. The
symptom sub-scale had demonstrated a change of 24.5% from
51% to 85.5%. The present study observed a 28.64% change
in ADL/functional disability sub-scale. Since the MCID is
not established for HOOS, it is difficult to comment on the
significance of the observed change. However this improvement
may have resulted from the replacement of damaged hip
with a new artificial joint. It is augmented by motor control
trainingwhich could have improved the balance between local
and global muscle system, preventing micro-trauma resulting
from an imbalanced muscle system in the hip. This explains the
lower pain level and optimized function.

Limitations of the Study

Since the present study had a small sample size the findings of
the study cannot be generalized.

Recommendations for Future Research

A Randomized controlled trial is recommended to evaluate
the role of motor control training alone in postoperative
rehabilitation following THR. The present study did not use
EMG analysis or ultrasonography of hip muscles to evaluate the
changes in the muscle structure and function. The use of either
can give a strong evidence to support the muscle recruitment as
well as muscle size changes.

Conclusion

The implementation of a 8 week motor control training for deep
external rotators of the hip with the standard THR rehabilitation
improves pain and functional outcomes post unilateral THR.